U.S. patent number 5,776,649 [Application Number 08/922,770] was granted by the patent office on 1998-07-07 for method of transferring toner to receiver with copolymer blend.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to John J. Fitzgerald, Louis Joseph Sorriero.
United States Patent |
5,776,649 |
Sorriero , et al. |
July 7, 1998 |
Method of transferring toner to receiver with copolymer blend
Abstract
The composition of the present invention is a miscible blend
comprising a first addition copolymer and a second addition
copolymer, each having a weight-average molecular weight of about
30,000 to 100,000 and a number-average molecular weight of about
5,000 to 50,000, and each comprising repeating units of (1) at
least one of an aromatic vinyl monomer of the structure, ##STR1##
where Ar is phenylene or naphthylene and R.sup.1 and R.sup.2 are H
or lower alkyl; and (2) at least one of (a) an acrylic ester of the
structure ##STR2## where R.sup.3 is linear or branched C.sub.1
-C.sub.10 alkyl and R.sub.4 is H or lower alkyl, or (b) a divinyl
compound of the structure ##STR3## where R.sup.5 and R.sup.6 are H,
Cl, or CH.sub.3. The polymer composition comprises a miscible blend
of the above-described first and second addition copolymers. The
first addition copolymer further comprises repeating units of an
acidic vinyl monomer, and the second addition copolymer further
comprises repeating units of a basic vinyl monomer. Also in
accordance with the present invention, an electrophotographic toner
receiver for thermally assisted transfer comprises a substrate
having a layer of a thermoplastic polymer composition on the
surface thereof. The polymer composition comprises a miscible blend
of the above-described first and second addition copolymers.
Further in accordance with the invention, a method comprises the
non-electrostatically transferring of small toner particles from
the surface of a photoconductive element to the described toner
receiver.
Inventors: |
Sorriero; Louis Joseph
(Rochester, NY), Fitzgerald; John J. (Clifton Park, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
24286853 |
Appl.
No.: |
08/922,770 |
Filed: |
September 3, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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572213 |
Dec 13, 1995 |
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Current U.S.
Class: |
430/125.6 |
Current CPC
Class: |
G03G
7/0006 (20130101); G03G 7/004 (20130101); Y10T
428/24802 (20150115); Y10T 428/31906 (20150401) |
Current International
Class: |
G03G
7/00 (20060101); G03G 013/16 () |
Field of
Search: |
;430/126 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
R M. Wiley, J. Colloid Science, vol. 9, 1954, pp. 427-437..
|
Primary Examiner: Martin; Roland
Attorney, Agent or Firm: Wells; Doreen M.
Parent Case Text
This is a Divisional of application U.S. Ser. No. 08/572,213, filed
13 Dec. 1995, pending.
Claims
We claim:
1. A method of nonelectrostatically transferring toner particles of
small size from the surface of a photoconductive element to an
electrophotographic toner receiver comprising a substrate having a
layer of a thermoplastic polymer composition on the surface
thereof, said polymer composition comprising a miscible blend of a
first addition copolymer and a second addition copolymer, each said
addition copolymer having a weight-average molecular weight of
about 30,000 to 100,000 and a number-average molecular weight of
about 5,000 to 50,000 and each comprising repeating units of
(1) at least one of an aromatic vinyl monomer of the structure,
##STR12## wherein Ar is phenylene or naphthylene and R.sup.1 and
R.sup.2 are H or lower alkyl; and
(2) at least one of
(A) an acrylic ester of the structure ##STR13## wherein R is linear
or branched C.sub.1 -C.sub.10 alkyl and R.sup.4 is H or lower
alkyl, or
(B) a divinyl compound of the structure ##STR14## wherein R.sup.5
and R.sup.6 are H, Cl, or CH.sub.3, said first addition copolymer
further comprising repeating units of an acidic vinyl monomer and
said second addition copolymer further comprising repeating units
of a basic vinyl monomer comprising the steps of:
(a) contacting said toner particles with said layer of
thermoplastic polymer composition of said receiver;
(b) heating said receiver to a temperature such that the
temperature of said layer of thermoplastic polymer composition of
said receiver during said transferring is at least about 5.degree.
C. above the glass transition temperature, T.sub.g, of said
thermoplastic composition; and
(c) separating said receiver from said photoconductive element at a
temperature above the T.sub.g of said thermoplastic composition,
but below the sticking temperature at which said thermoplastic
composition begins to adhere to said photoconductive element,
whereby virtually all of said toner particles are transferred from
the surface of said element to the layer of thermoplastic polymer
composition of said receiver.
2. The method of claim 1, wherein the glass transition temperature,
T.sub.g, of said thermoplastic composition is about 50.degree. to
60.degree. C.
3. The method of claim 1, wherein the difference between the
temperature during said transferring and the sticking temperature
comprises a transfer latitude, said transfer latitude comprising at
least about 13.degree. C.
4. The method of claim 3, wherein said transfer latitude comprises
at least about 18.degree. C.
5. The method of claim 1, wherein said thermoplastic composition
comprises a miscible blend of a first addition copolymer and a
second addition copolymer, said first addition copolymer comprising
styrene, butyl acrylate, and methacrylic acid, and said second
addition copolymer comprising styrene, butyl acrylate, and
4-vinylpyridine.
6. The method of claim 1, wherein said thermoplastic composition
comprises a miscible blend of a first addition copolymer and a
second addition copolymer, said first addition copolymer comprising
3-methylstyrene, 4-methylstyrene, 2-ethylhexylacrylate, and
methacrylic acid, and said second addition copolymer comprising
3-methylstyrene, 4-methylstyrene, 2-ethylhexyl acrylate, and
4-vinylpyridine.
Description
FIELD OF THE INVENTION
This invention relates to novel copolymer blends and, more
particularly, to the use of such blends as coatings for
electrophotographic toner receivers.
BACKGROUND OF THE INVENTION
It is possible by electrophotography to produce images of high
resolution and low granularity that are of comparable quality to
images produced by photography or lithography. To obtain copies or
images of such high quality, the toner particles must be of small
size, e.g., of 3 to 5 .mu.m mean volume weighted diameter. However,
the image quality is poor when the electrophotographic process uses
the conventional electrostatic transfer method for transferring the
small toner particles from the surface of the photoconductive
element to the toner receiver. It is believed that the surface
forces holding the small toner particles to the photoconductor
surface dominate over the electrostatic transfer forces and prevent
adequate transfer.
Recent patents, for example, U.S. Pat. No. 4,927,727, the
disclosure of which is incorporated herein by reference, have
disclosed that images made with small toner particles can be
transferred with high efficiency by thermally assisted transfer
(TAT). In the TAT method, the receiver is heated, e.g., to
60.degree. to 90.degree. C., and is pressed against the toner
particles on the surface of the photoconductive element. The heat
sinters the thermoplastic toner particles, causing them to stick
together and to the receiver. The element and receiver are then
separated and the toner image is fixed, e.g., thermally fused to
the receiver.
To improve the transfer of toner from the photoconductive element
to the receiver, a number of modifications have been made in the
TAT process. For example, U.S. Pat. No. 4,968,578 describes
applying to the receiver a thermoplastic coating and a layer of a
release agent. This technique improves the image quality but the
releasing agent can create problems, as mentioned in U.S. Pat. No.
5,043,242. The latter patent, the disclosure of which is
incorporated herein by reference, discloses a receiver coating of a
particular surface energy that provides good transfer without a
release agent. Likewise, U.S. Pat. Nos. 5,037,718 and 5,045,424,
the disclosures of which are incorporated herein by reference,
disclose particular polymeric coatings for the receiver that
provide good transfer without a release agent. The materials and
procedures of these patents provide important advantages, but
further improvement in the TAT process is desirable.
One need in the TAT process is for a toner receiver that will have
a wider transfer latitude than materials heretofore available. By
"transfer latitude" is meant the difference between (a) the
"transfer temperature," at which the polymer coating on the
receiver surface softens enough that toner particles on the
photoconductive element will adhere to or become partially embedded
in the polymer coating and thus transfer to the receiver, and (b)
the "sticking temperature," at which the receiver begins to stick
to the photoconductive element. More specifically, the sticking
temperature is the highest temperature at the nip of an
electrophotographic TAT apparatus where contact of the receiver and
photoconductor surfaces in an untoned area results in no damage to
either surface upon separation. Although not wishing to be bound by
theoretical considerations, applicants believe that the sticking
temperature is related to the dynamic mechanical behavior of the
receiver thermoplastic polymer composition, and specifically to the
width at half-height of the "tan .delta.," which is the ratio of
the loss modulus to the storage modulus of the composition in the
melt phase. This ratio, which is also referred to as the
"dissipation factor," measures the inability of a material to
behave in an elastic manner. This subject is discussed in J. D.
Ferry, Viscoelastic Properties of Polymers, 2nd Ed., John Wiley and
Son, 1970, p. 48, and in A. Rubin, The Elements of Polymer Science
and Engineering, Academic Press, 1982, p. 417.
The transfer temperature is the lowest temperature at which toner
particles forming a latent image on a photoconductive element will
adhere to the thermoplastic polymeric composition of the receiver
and be transferred from the photoconductor to the receiver surface
with an efficiency of at least 98 percent. The transfer temperature
is sensitive to both the T.sub.g and molecular weight of the
receiver polymer.
In practice, the T.sub.g of the receiver polymeric composition is
preferably at least about 50.degree. C., more preferably at least
about 52.degree. C. The transfer temperature is generally 8.degree.
to 15.degree. C. higher than the T.sub.g, typically in the
60.degree. to 75.degree. C. range. A sticking temperature range of
about 70.degree. to 85.degree. C. would correspond to a transfer
latitude of 10.degree. C., the minimum required to ensure good
process control and high image quality.
Previously known receiver materials often exhibit a transfer
latitude of 5.degree. C. or less. In accordance with the present
invention, a novel polymeric blend used to form a coating for the
toner receiver has a high sticking temperature and a transfer
latitude greater than about 12.degree. C.
As stated by P. J. Flory in his treatise entitled "Principles of
Polymer Chemistry" (1953), "It is well known that, regarding the
mixing of thermoplastic polymers, incompatibility is the rule and
miscibility and even partial miscibility is the exception." This
statement and others relating to the rarity of miscible polymer
blends are quoted in U.S. Pat. No. 5,084,526, the disclosure of
which is incorporated herein by reference. The Flory quotation
indicates the unexpectedness of the properties of the novel
miscible polymer blend of the present invention, in particular, its
optical clarity and its characterization by a single glass
transition temperature (T.sub.g), as measured by differential
scanning calorimetry. This is a property of major importance in
forming coatings for receivers for the TAT process. Even though a
polymer composition might have certain good properties, it would
not be a suitable coating material for a TAT receiver if it
exhibited more than a single T.sub.g.
BRIEF SUMMARY OF THE INVENTION
The composition of the present invention comprises a novel
thermoplastic blend of two linear addition copolymers. One of these
copolymers includes repeating units of an acidic monomer, while the
other includes repeating units of a basic monomer. Unlike most
polymer blends, the novel composition is a miscible blend having a
single glass transition temperature, T.sub.g, and, when used as a
surface coating for a toner receiver in thermally assisted transfer
of toner, has a wide transfer latitude. More particularly, the
composition of the invention is a miscible blend comprising a first
addition copolymer and a second addition copolymer, each having a
weight-average molecular weight of about 30,000 to 100,000 and a
number-average molecular weight of about 5,000 to 50,000, and each
comprising repeating units of (1) at least one of an aromatic vinyl
monomer of the structure, ##STR4## where Ar is phenylene or
naphthylene and R.sup.1 and R.sup.2 are H or lower alkyl; and (2)
at least one of (a) an acrylic ester of the structure ##STR5##
where R.sup.3 is linear or branched C.sub.1 -C.sub.10 alkyl and
R.sub.4 is H or lower alkyl, or (b) a divinyl compound of the
structure ##STR6## where R.sup.5 and R.sup.6 are H, Cl, or
CH.sub.3. The first addition copolymer further comprises repeating
units of an acidic vinyl monomer, and the second addition copolymer
further comprises repeating units of a basic vinyl monomer.
Also in accordance with the present invention, an
electrophotographic toner receiver for thermally assisted transfer
comprises a substrate having a layer of a thermoplastic polymer
composition on the surface thereof. The polymer composition
comprises a miscible blend of the above-described first and second
addition copolymers.
Further in accordance with the present invention, a method of
nonelectrostatically transferring toner particles of small size
from the surface of a photoconductive element to the
above-described electrophotographic toner receiver comprises the
steps of (a) contacting the toner particles with the layer of
thermoplastic polymer composition of the receiver; (b) heating the
receiver to a temperature such that the temperature of the layer of
thermoplastic polymer composition of the receiver during the
transferring is at least 5.degree. C. above the glass transition
temperature, T.sub.g, of the thermoplastic composition; and (c)
separating the receiver from the photoconductive element at a
temperature above the T.sub.g of the thermoplastic composition,
whereby virtually all of the toner particles are transferred from
the surface of the element to the layer of thermoplastic polymer
composition of the receiver.
DETAILED DESCRIPTION OF THE INVENTION
The novel polymer composition that forms the surface layer or
coating for the TAT receiver of the invention is a miscible blend
comprising two addition polymers. As pointed out in U.S. Pat. No.
5,084,526 cited above, miscible blends of polymers are rare. In
accordance with the present invention, however, such a miscible
blend is formed when the monomers described herein are employed;
the resulting miscible blend has a single glass transition
temperature (T.sub.g). Without the valuable property of a single
T.sub.g, the blend would not be of practical value as a receiver
layer in the thermally assisted transfer of fine toner
particles.
Of equal importance is another unexpected property of the blend,
namely, its wide transfer latitude in the TAT process. As will be
demonstrated in examples hereinafter, the transfer latitude of the
polymer blends of the invention is at least about 12.degree. C. and
can be greater than 26.degree. C. Thus, with the receiver layers of
the invention it is possible to transfer toner from the
photoconductive element to the receiver over a wide temperature
range, without causing the receiver to stick to the photoconductive
element.
In accordance with the present invention, the miscible blend
comprises a first addition copolymer and a second addition
copolymer, each having a weight-average molecular weight of about
30,000 to 100,000 and a number-average molecular weight of about
5,000 to 50,000, and each comprising repeating units of (1) at
least one of an aromatic vinyl monomer of the structure, ##STR7##
where Ar is phenylene or naphthylene and R.sup.1 and R.sup.2 are H
or lower alkyl; and (2) at least one of (a) an acrylic ester of the
structure ##STR8## where R.sup.3 is linear or branched C.sub.1
-C.sub.10 alkyl and R.sub.4 is H or lower alkyl, or (b) a divinyl
compound of the structure ##STR9## where R.sup.5 and R.sup.6 are H,
Cl, or CH.sub.3. The first addition copolymer further comprises
repeating units of an acidic vinyl monomer, and the second addition
copolymer further comprises repeating units of a basic vinyl
monomer. The weight-average and number-average molecular weights of
the addition copolymers are determined by gel permeation
chromatography, as discussed in column 11 of the previously
mentioned U.S. Pat. No. 5,045,424, the disclosure of which is
incorporated herein by reference.
The acidic vinyl monomer comprises a compound having the structure
##STR10## where Ar is phenylene or naphthylene, R.sup.1 is H or
CH.sub.3, R.sup.2 is H or C.sub.1 -C.sub.6 alkyl, R.sup.3 is
C.sub.2 -C.sub.6 alkylene, and R.sup.4 is --COOH or --SO.sub.3 H.
Methacrylic acid and acrylic acid are especially preferred,
methacrylic acid being most preferred.
The basic vinyl compound comprises 2-vinylpyridine,
4-vinylpyridine, or a compound having the structure ##STR11## where
R.sup.1 is H or CH.sub.3, R.sup.2 is H or C.sub.1 -C.sub.6 alkyl,
R.sub.3 is C.sub.2 -C.sub.6 alkylene, and R.sub.4 and R.sub.5 are
each C.sub.1 -C.sub.4 alkyl. 4-Vinylpyridine and 2-vinylpyridine
are especially preferred, 4-vinylpyridine being most preferred.
The first addition copolymer of the miscible blend comprises one to
25 weight percent, preferably 2 to 10 weight percent, and most
preferably 2.5 to 5 weight percent of the acidic vinyl monomer. The
second addition copolymer comprises one to 25 weight percent,
preferably 20 to 10 weight percent, and most preferably 2.5 to 5
weight percent of the basic vinyl monomer.
The weight ratio of aromatic vinyl monomer to acrylic ester or
divinyl compound in the first and second addition copolymers is
from about 20:1 to 1:20, preferably from about 8:1 to 1:2, and most
preferably from about 4:1 to 1:1. The weight ratio of first
addition polymer to second addition polymer in the miscible blend
is preferably about 1:1.
The aromatic vinyl monomers utilized to form the first and second
addition copolymers are preferably styrene compounds, especially
styrene, 3-methylstyrene, 4-methylstyrene, .alpha.-methylstyrene,
4-t-butylstyrene, or mixtures thereof. Most preferred are styrene
or a commercially available mixture of 3-and 4-methylstyrene,
sometimes referred to as "vinyltoluene."
Divinyl compounds used to prepare the addition copolymers
comprising the miscible blend of the invention include
1,3-butadiene and substituted derivatives thereof, including
2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene,
2,3-dimethyl-1,3-butadiene, and mixtures thereof. 1,3-Butadiene is
especially preferred.
The acrylic ester monomers employed in the formation of the
addition copolymers are preferably esters of acrylic acid,
including ethyl acrylate, butyl acrylate, hexyl acrylate,
2-ethylhexyl acrylate, and mixtures thereof. Butyl acrylate and
2-ethylhexyl acrylate are especially preferred.
As previously noted, the miscible blends of the invention exhibit a
single glass transition temperature, T.sub.g, which falls between
the T.sub.g 's of the first and second copolymers comprising the
blend. The glass transition temperature, T.sub.g, of the miscible
blends of the invention preferably lie between about 40.degree. and
70.degree. C., most preferably between about 50.degree. and
60.degree. C., as measured by differential scanning
calorimetry.
The thermally assisted transfer (TAT) of toner particles of very
small size having a mean volume diameter of less than about 8 .mu.m
(as measured by commercially available particle diameter measuring
devices, e.g., a Coulter Multisizer, sold by Coulter Inc.) is
described in the previously mentioned U.S. Pat. Nos. 4,927,727 and
5,043,242, the disclosures of which are incorporated herein by
reference. In a TAT process, the toner receiver is preheated to a
temperature that is adequate to fuse the transferred toner
particles at their points of contact but not so high as to cause
melting or coalescence of the particles. Pressure aids in the
transfer of the toner particles to the receiver; an average nip
pressure of about 135 to 1000 kPa is preferred. Residence time of
the receiver in the nip is very short, typically on the order of
about 15 milliseconds.
The nip temperature range for the thermally assisted toner transfer
process is limited by the properties of the photoconductor, the
toner particles, including the T.sub.g of the toner binder, and the
receiver, including the T.sub.g of the thermoplastic polymer
composition on its substrate surface. With respect to the
photoconductor, increasing its temperature causes an increase in
the rate of dark decay. The toner particles employed comprise
polymeric binders generally having T.sub.g 's of about 40.degree.
to 120.degree. C., preferably about 50.degree. to 100.degree. C.
Useful toner binders, including the preferred polymers and
copolymers of styrene and acrylic ester monomers, are discussed in
columns 22-23 of U.S. Pat. No. 5,045,424 and in columns 5-6 of U.S.
Pat. No. 4,968,578, the disclosures of which are incorporated
herein by reference. As previously noted, the miscible blends in
the toner receiver of the present invention have T.sub.g 's of
about 40.degree. to 70.degree. C., preferably about 50.degree. to
60.degree. C., as determined by differential scanning
calorimetry.
As previously discussed, the transfer latitude is a temperature
range defined at its lower end by the transfer temperature, the
minimum at which acceptable transfer of toner from the
photoconductive element to the receiver can be achieved, and at its
higher end by the sticking temperature, at which the thermoplastic
composition of the receiver begins to adhere to the photoconductive
element. The transfer temperature is a function of various receiver
properties, including the molecular weight and T.sub.g of the
thermoplastic composition. In general, the transfer temperature is
about 8.degree. to 15.degree. C. higher than the T.sub.g of the
thermoplastic composition on the receiver substrate. The sticking
temperature depends at least partially on the elastic properties of
the receiver and the adhesive forces between the photoconductor and
the thermoplastic composition.
To ensure adequate process control and acceptable image quality,
the transfer latitude should be at least about 10.degree. C. The
present invention provides a toner receiver comprising
thermoplastic compositions with substantially elevated sticking
temperatures compared to previously known compositions. This
results in greatly improved transfer latitude of at least about
13.degree. C. and, in preferred embodiments, at least about
18.degree. C.
The electrophotographic toner receiver of the invention is formed
by applying the miscible blend to a substrate in various ways known
in the art, for example, by solvent coating or melt extrusion.
Coating aids such as a polymethylphenylsiloxane (for example,
DC-510.TM. having a methyl:phenyl ratio of 23:1, available from
Dow-Coming Company) can be used to facilitate the coating of the
blend on the substrate. The substrate can be a transparent film or,
preferably, paper. More preferably, the paper substrate is coated
on each side with a layer of polyolefin. Procedures for forming
receivers are discussed in columns 15-19 of the previously
mentioned U.S. Pat. No. 5,045,424, the disclosure of which is
incorporated herein by reference.
The addition polymers comprising the miscible blend of the
invention can be prepared by a variety of methods known to those
skilled in the art. One convenient technique is particulate
stabilized suspension (limited coalescence) polymerization, as
described in R M. Wiley, J. Colloid Science, Vol. 9, p. 427 (1954),
the disclosure of which is incorporated herein by reference.
Following washing and drying, a first addition polymer having
repeating units of an acidic vinyl monomer can be blended with a
second addition polymer having repeating units of a basic vinyl
monomer. Blending can be accomplished either by melting the two
copolymers together or by dissolving them in a suitable solvent.
Preferably, the blend contains the two copolymers in an
approximately 1:1 weight ratio.
The following examples further illustrate the invention.
EXAMPLE 1
Preparation of Copolymers
Copolymers were prepared by the following particulate stabilized
suspension polymerization procedure.
An organic phase consisting of a total of 100 grams of the desired
monomers and 2.0 grams of the polymerization initiator Vazo 67.TM.
(available from Dupont) was emulsified, using a Waring blender,
with an aqueous phase containing 200 grams of distilled water, 2.0
grams of a 10% (w/w) aqueous solution of poly(methylaminoethylene
adipate) (a condensation polymer prepared in-house by conventional
methods), and 2.0 grams of Ludox.TM. 50% colloidal silica
(available from Dupont), and buffered to pH 4.0 with 10.0 grams of
phthalate buffer solution (from VWR Scientific). The resulting
emulsion was placed in a reaction vessel equipped with a stirrer,
condenser, and nitrogen inlet, and heated, with gentle stirring, at
a temperature of about 77.degree. C. for 16 hours. The mixture was
then vented, heated to 90.degree. C., and flushed with nitrogen to
remove residual monomers, then cooled, and filtered. The collected
polymeric product was washed with water, then dried in a vacuum
oven.
Number-average (M.sub.n) and weight-average (M.sub.w) molecular
weights were determined as polystyrene equivalent molecular weights
by gel permeation chromatography as described in the previously
mentioned U.S. Pat. No. 5,045,424. Glass transition temperatures
were measured by differential scanning calorimetry, using a Perkin
Elmer DSC-4 apparatus in combination with a Perkin Elmer 3600 data
station. The temperature was calibrated with an indium standard,
and samples were typically run between -20.degree. and 100.degree.
C. at 10.degree. C. per minute. Onset, midpoint, and terminal
points of the transition were determined; the T.sub.g values listed
represent the midpoint values of the measurements.
Table 1 below includes the component monomers, and M.sub.n,
M.sub.w, and T.sub.g values of the copolymers prepared as described
above.
TABLE 1
__________________________________________________________________________
Monomer (parts by weight) Vinyl- Butyl 2-Ethylhexyl 4-Vinyl-
Methacrylic Copolymer Styrene toluene* acrylate acrylate pyridine
acid M.sub.n M.sub.w T.sub.g (.degree.C.)
__________________________________________________________________________
1 70 -- 30 -- -- -- 39,800 86,700 52 2 47.5 -- 55 -- -- 2.5 38,700
85,800 29 3 80 -- 17.5 -- 2.5 -- 21,900 59,000 69 4 75 -- 20 -- --
2.5 23,600 68,000 61 5 50 -- 45 -- 2.5 -- 5,800 48,000 20 6 -- 85
-- 10 -- 5.0 37,300 79,400 84 7 -- 62.5 -- 32.5 5.0 -- 28,300
69,600 31 8 -- 83 -- 17 -- -- 38,400 87,500 54
__________________________________________________________________________
*mixture of 3 and 4methylstyrene (from Dow Chemical Co.)
EXAMPLE 2
Preparation of Toner Receivers with Thermoplastic Copolymer Surface
Layers
The following general procedure was used to prepare receivers
having copolymer surface layers comprising miscible blends of the
invention. Control receivers with surface layers containing prior
art polymeric materials were also prepared.
The copolymer material to be coated was dissolved in methylene
chloride containing 0.24 weight percent (based on the total weight
of the solution) of Dow-Corning DC-510.TM. polymethylphenylsiloxane
coating agent. The solution, containing 10 weight percent of
copolymer, was coated on a polyethylene coated flexible paper
substrate that had been corona treated to promote adhesion. The
solvent was evaporated, leaving a 10 .mu.m-thick layer of polymer
on the substrate.
Transfer temperatures for the toner receivers so prepared were
determined by the following procedure:
Each receiver was used in an electrophotographic apparatus as
described in U.S. Pat. No. 4,473,029, the disclosure of which is
incorporated herein by reference. The photoconductive element of
the apparatus was provided with an organic photoconductor, as
described in U.S. Pat. No. 5,213,927, the disclosure of which is
incorporated herein by reference. A styrene-butyl acrylate toner
having a binder T.sub.g of 62.degree. C. and a particle size of 3.5
.mu.m was employed; there was no electrostatic bias between the
receiver and the photoconductive element.
The front surface of the receiver was heated prior to transfer of
the toner particles from the photoconductor to the receiver, which
was accomplished by passage through the nip region of a pair of
compression rollers, as described in U.S. Pat. No. 5,308,733, the
disclosure of which is incorporated herein by reference. The heated
roller comprised an aluminum core coated with Teflon. Air pressure
to the unheated roller was sufficient to produce a force at the nip
of 7.0.times.10.sup.3 N/m along the length of the transfer rollers.
The passage speed varied from 3.18 to 4.0 cm/sec.
Immediately following transfer, the receiver was separated from the
photoconductor. The toner image on the receiver was ferrotyped by
casting it against a sheet of Kapton-H.TM. and passing the receiver
and the Kapton-H.TM. sheet at a speed of about 0.5 cm/sec through a
pair of hard compression rollers, one heated to a temperature of
about 110.degree. C. and the other unheated. Three images were
sequentially transferred in register. The minimum temperature of
the receiver surface at the nip needed to effect transfer of the
smaller toner particles from the photoconductor to a given receiver
with at least 98 percent efficiency is defined as the transfer
temperature for that receiver.
Sticking temperatures were determined using the same apparatus as
for the transfer temperature measurements, but no toner particles
were employed. The receiver surface was heated and contacted with
the photoconductive element at the nip. The imminence of the
sticking temperature was signaled by the sound of the
photoconductor and receiver surfaces separating. The minimum
temperature at which the separation caused damage to the surface of
a receiver and/or the photoconductor is taken as the sticking
temperature for that receiver.
Transfer and sticking temperature data, along with the glass
transition temperature for the miscible blends of the invention and
the control copolymers are given in Table 2 below.
TABLE 2
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Transfer Sticking Transfer Receiver Copolymers T.sub.g (.degree.C.)
temperature (.degree.C.) temperature (.degree.C.) latitude
(.degree.C.)
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I 4 and 5* 53 65 87 22 II 2 and 3* 54 72 >90 >18 III 6 and 7*
54 69 >90 >21 IV (control) 1 52 64 69 5 V(control) 8 54 64 72
8 VI (control) S5E** 54 69 81 12
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*blends at 1:1 weight ratio **styrene1,3-butadiene (85/15)
copolymer available as Pliolite S5E .TM. from Goodyear Co.
As shown in Table 2, receivers I, II, and III, which contain
miscible 1:1 (by weight) blends of copolymers listed in Table 1,
all had very similar glass transition temperature
(53.degree.-54.degree. C.). Their measured transfer temperatures
lay between 65.degree. and 72.degree. C., and they all exhibited
sticking temperatures of at least 87.degree. C. These results
translate to a transfer latitude of more than 18.degree. C. in all
cases.
Control receivers IV, V, and VI, each comprising a layer of a
single copolymer, exhibited glass transition temperatures very
nearly the same as those of the miscible blends employed in
receivers I, II, and III. The measured transfer temperatures of
control receivers IV, V, and VI were in the range of
64.degree.-69.degree. C., similar to those of the receivers of the
invention. Sticking temperatures for IV, V, and VI, however, were
well below those of receivers I, II, and III, and so the transfer
latitude for the control receivers was distinctly inferior, falling
in the range of 5.degree.-12.degree. C.
Thus, the results of Table 2 strikingly demonstrate the substantial
and unexpected advantage in transfer latitude of toner receivers
formed from the miscible copolymer blends of the present invention,
compared with prior art polymeric materials.
The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *